button on-Click event

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Java

Mobile

Blackberry

class checkPlay extends MainScreen{
        FieldChangeListener listener;

        public checkPlay() {
                setTitle("Testing");
        listener = new FieldChangeListener() {
                public void fieldChanged(Field field, int context) {
                        ButtonField playButton= (ButtonField) field;
                    signUp sinup=new signUp();
                    sinup.newMethod();
                    
                }
            };
            ButtonField playButton = new ButtonField("Test Button");

            playButton.setChangeListener(listener);
            add(playButton);
        }
}
class signUp extends MainScreen{
        public signUp(){
               // setTitle("Sign Up For New Account");
                 BasicEditField firstName = new BasicEditField("First Name*: ", "");
                 BasicEditField lastName = new BasicEditField("Last Name*: ", "");
                 EmailAddressEditField Email = new EmailAddressEditField("Email*: ", "");
                 PasswordEditField password = new PasswordEditField("Password*: ", "",100,                                                                     PasswordEditField.FILTER_DEFAULT);
                 PasswordEditField confirmPassword = new PasswordEditField("Confirm Password*: ", "",100,
                                  PasswordEditField.FILTER_DEFAULT);
                 DateField birthDay=new DateField("Birthday: ",System.currentTimeMillis(),DateField.DATE);
                 LabelField gender = new LabelField("Gender", LabelField.ELLIPSIS | LabelField.USE_ALL_WIDTH);
                 RadioButtonGroup rbg = new RadioButtonGroup();
                 CheckboxField condition = new CheckboxField("I agree with the conditions", false);
                // ButtonField joinButton = new ButtonField("JOIN NOW", ButtonField.FIELD_LEFT);


             ButtonField joinButton = new ButtonField("JOIN NOW",ButtonField.FIELD_LEFT);
           
                 add(firstName);
                 add(lastName);
                 add(Email);
                 add(password);
                 add(confirmPassword);
                 add(birthDay);
                 add(gender);
                 add(new RadioButtonField("Male",rbg,true));
                 add(new RadioButtonField("Female",rbg,false));
                  add(condition);
                 add(joinButton);


        }
        void newMethod(){
                setTitle("Dhoni");
        }
}

I want to call newMethod class by clicking a button.
I have put a button in checkPlay class and after clicking that button, I should call to newMethod.
But this code is not giving the output correctly. Is there any problem with the code??
Please help me